1. Field of Invention
The present invention relates to a display medium and a display method. In particular, the invention relates to a display medium and a display method using charged mobile fine particles widely usable as optical elements such as dimmer glass, a dimmer element, and a display element.
2. Description of the Related Art
Along with the advancement of the highly information-based society, needs of electronic paper systems, color display systems, and large surface area display systems have been increased. As technologies to realize these systems, display technologies such as CRT, liquid crystal, EL, LED, and plasma have been developed. Further, besides these self-light-emitting systems, developments of reflection type display systems, which can save electric power consumption and scarcely cause an uncomfortable feeling to eyes of human being, have been investigated. As the reflection type display system, a reflection type liquid crystal technique is dominantly used.
On the other hand, while needs for the next generation of electronic paper display systems are very high, the present situation is that hopeful techniques to satisfy the needs have not established yet. Examples of known candidate methods supposed to be practically usable include an electrophoresis method, a liquid crystal method, and an organic EL method.
Since a liquid crystal method is a filter method, it has a problem that the medium thickness and weight are difficult to decrease. Since an organic EL method is a self-light-emitting type, there is a problem that it has no memory and its uses are thus limited within a narrow range.
As a display element using an electrophoresis method, the following techniques have been disclosed.
A method of using microcapsules arranged between a pair of electrodes, wherein a dispersion media and electrophoresis particles are encapsulated in the microcapsules, has been disclosed. Also, a magnetophoresis method using microcapsules encapsulating a magnetic fluid has been reported.
Further, a method of selectively driving plural kinds of colored particles disposed in a mixed state in a single microcapsule has been disclosed.
However, since all of these methods use microcapsules, it is difficult to carry out fine dot display and full color display. In the case of a conventionally-known method, it was difficult to selectively drive the particles in principle.
Further, a structure has been described in which approximately the same amount of charged electrophoresis particles are each disposed in a plurality of sections divided along the surfaces of a pair of substrates having a prescribed distance therebetween, and the dispersion medium is blue and the electrophoresis particles are black. It has been reported that the display quality can be improved by the structure.
However, the structure has difficulty in full color display, and must have a parallel arrangement because if layered, color display by a subtractive color-mixing method using combination of particles in the respective layers cannot be carried out. As a result, the apparatus becomes complicated.
Further, a method for carrying out color display by arranging the cells or microcapsules expressing a plurality of colors in parallel has been disclosed (. In this method, owing to the parallel arrangement, high resolution and sufficient contrast cannot be achieved.
Further, a method of layering two or more layers of light transmitting electrophoresis parts containing particles and/or a medium in vertical direction has been disclosed. However, dyes are used for coloring the particles and therefore no sufficient coloration density is obtained.
Further, a method has been disclosed wherein the cells having two display electrodes arranged at overlaying positions, two collection electrodes, and two kinds of light transmitting colored particles are layered or parallel arranged. However, since relatively large particles colored by dyes are employed, no sufficient color density can be obtained and stability of the coloring agents are problematic.
Furthermore, a method where particles are moved in a direction vertical to a substrate has been disclosed, wherein the particles are colorless in a dispersed state and show a color of particles in a agglomerated state. However, in this method, since a predetermined color is obtained by agglomerating particles, a plurality of cells wherein the particles are encapsulated has to be prepared and area gradation has to be applied in order to realize multi-colorization and multi-gradations. Accordingly, since it is difficult to represent one pixel with one cell and to realize colorization in one pixel, the method has problems in that high resolution is difficult to obtain and sufficient contrast cannot be obtained.